The present invention relates to golf balls, and more particularly, to a golf ball having improved dimples.
Golf balls generally include a spherical outer surface with a plurality of dimples formed thereon. Conventional dimples are circular depressions that reduce drag and increase lift. These dimples are formed where a dimple wall slopes away from the outer surface of the ball forming the depression.
Drag is the air resistance that opposes the golf ball""s flight direction. As the ball travels through the air, the air that surrounds the ball has different velocities thus, different pressures. The air exerts maximum pressure at a stagnation point on the front of the ball. The air then flows around the surface of the ball with an increased velocity and reduced pressure. At some separation point, the air separates from the surface of the ball and generates a large turbulent flow area behind the ball. This flow area, which is called the wake, has low pressure. The difference between the high pressure in front of the ball and the low pressure behind the ball slows the ball down. This is the primary source of drag for golf balls.
The dimples on the golf ball cause a thin boundary layer of air adjacent to the ball""s outer surface to flow in a turbulent manner. Thus, the thin boundary layer is called a turbulent boundary layer. The turbulence energizes the boundary layer and helps move the separation point further backward, so that the layer stays attached further along the ball""s outer surface. As a result, a reduction in the area of the wake, an increase in the pressure behind the ball, and a substantial reduction in drag are realized. It is the circumference of each dimple, where the dimple wall drops away from the outer surface of the ball, which actually creates the turbulence in the boundary layer.
Lift is an upward force on the ball that is created by a difference in pressure between the top of the ball and the bottom of the ball. This difference in pressure is created by a warp in the airflow that results from the ball""s backspin. Due to the backspin, the top of the ball moves with the airflow, which delays the air separation point to a location further backward. Conversely, the bottom of the ball moves against the airflow, which moves the separation point forward. This asymmetrical separation creates an arch in the flow pattern that requires the air that flows over the top of the ball to move faster than the air that flows along the bottom of the ball. As a result, the air above the ball is at a lower pressure than the air underneath the ball. This pressure difference results in the overall force, called lift, which is exerted upwardly on the ball. The circumference of each dimple is important in optimizing this flow phenomenon, as well.
By using dimples to decrease drag and increase lift, almost every golf ball manufacturer has increased their golf ball flight distances. In order to optimize ball performance, it is desirable to have a large number of dimples, hence a large amount of dimple circumference, which is evenly distributed around the ball. In arranging the dimples, an attempt is made to minimize the space between dimples, because such space does not improve aerodynamic performance of the ball. In practical terms, this usually translates into 300 to 500 circular dimples with a conventional sized dimple having a diameter that typically ranges from about 0.100 inches to about 0.180 inches.
When compared to one conventional size dimple, theoretically, an increased number of small dimples may enhance aerodynamic performance by increasing total dimple circumference. However, in reality small dimples are not always very effective in decreasing drag and increasing lift. This results at least in part from the susceptibility of small dimples to paint flooding. Paint flooding occurs when the paint coat on the golf ball partially fills the small dimples, and consequently decreases the dimple""s aerodynamic effectiveness. On the other hand, a smaller number of large dimples also begin to lose effectiveness. This results from the circumference of one large dimple being less than that of a group of smaller dimples.
One attempt to improve the aerodynamics of a golf ball is to create a ridge-like polygon inside a non-circular dimple and near the center of the dimple, where the edges of the polygon are positioned below the un-dimpled surface of the ball. This approach is described in U. S. Pat. No. 6,315,686 B1 and U.S. patent application publication no. 2002/0025864 A1. The ""686B1 and ""864A1 references theorize that the polygonal ridges generate the turbulent boundary layer during low and intermediate ball velocities, and the non-circular dimples with the polygonal centers are used in conjunction with the conventional circular dimples on a golf ball. U.S. Pat. No. 4,869,512 also discloses the use of non-circular dimples with conventional circular dimples to improve aerodynamic performance of a golf ball. These non-circular dimples have shapes that include triangular, petal, oblong, and partially overlapping circles, among others. Additionally, U.S. Pat. No. 5,377,989 discloses non-circular isodiametrical dimples, wherein the dimples have an odd number of curved sides.
Another approach for improving the aerodynamics of a golf ball is suggested in U.S. Pat. No. 6,162,136, wherein a preferred solution is to minimize the land surface or undimpled surface of the ball to maximize dimple coverage. One way of maximizing the dimple coverage of the ball is to pack closely together circular dimples having various sizes, as disclosed in U.S. Pat. Nos. 5,957,786 and 6,358,161. In practice, the circular dimple coverage is limited to about 85% or less when non-overlapping dimples are used. Another attempt to maximize dimple coverage is to use polygonal dimples with polyhedron dimple surfaces, i.e., dimple surfaces constructed from planar surfaces, as suggested in a number of patent references including U.S. Pat. Nos. 6,290,615B1, 5,338,039, 5,174,578, 4,090,716, and 4,830,378, among others. Theoretically, higher dimple coverage is attainable with these polygonal dimples. However, it has been demonstrated that polygonal dimples with polyhedron dimple surfaces do not achieve performance improvements commensurate with their coverage improvements. It is believed that the linear edges of the polygonal dimples and the connecting sharp apices generate more drag than the curved edges of the circular dimples.
Hence, there remains a need in the art for a golf ball that has a high dimple coverage and superior aerodynamic performance.
The present invention is directed to a golf ball with improved dimples.
The present invention is also directed to a golf ball with improved aerodynamic characteristics.
The present invention is also directed to an arrangement of the improved dimples on a golf ball.
The present invention is directed to a dimple comprising a plurality of lobes positioned radially around the center of the dimple, wherein each lobe is defined by a circumferential segment and the circumferential segments define at least a part of the perimeter of the dimple. Each lobe comprises a first curved profile extending from the circumferential segment to the center of the dimple and the first curved profile of each lobe abuts each other in an uninterrupted manner. The lobes may be further defined by spoke-like ridges positioned between adjacent lobes. These spoke-like ridges may extend from the perimeter toward the center of the dimple or to the center of the dimple. Each lobe further comprises a second curved profile extending across the width of the lobe. Alternatively, the portions of the perimeter where the circumferential segments abut can be rounded. Additionally, the size, shape and/or angular spacing of the lobes on a single dimple may vary.
The curvature or prominence of the lobes can be defined by a ratio of an inside radius (Ri) to an outside radius (Ro). The inside radius extends from the center to a trough or a location on the lobe radially closest to the center. The outside radius extends from the center to an apex point of the lobe. In accordance to one aspect of the present invention, the inventive dimple includes uniform multi-lobed dimples. The inside radius and outside radius are constant for all these lobes, and the prominence of each lobe is the same as that for the other lobes in the same dimple. The prominence ratio for uniform lobes is less than 1.0. Preferably, this ratio is between about 0.70 and about 0.95; more preferably the ratio is between about 0.75 and about 0.90; and most preferably the ratio is between about 0.80 and about 0.90.
In accordance to another aspect of the present invention, the inventive dimple also includes non-uniform multi-lobed dimples. These non-uniform multi-lobed dimples can be either concentric or eccentric. Concentric non-uniform multi-lobed dimples include dimples with the center of Ri coincides with the center of Ro, and eccentric non-uniform multi-lobed dimples include dimples with the center of Ri being spaced apart from the center of Ro.
Concentric non-uniform multi-lobed dimples may have a constant Ri and a constant Ro. Additionally, concentric non-uniform multi-lobed dimples may include those with a constant Ri and varying Ro, those with varying Ri and constant Ro, and those with varying Ri and varying Ro. Although, the prominence of each lobe may be different than other lobes in the same dimple, the prominence ratio for the concentric non-uniform multi-lobed dimple is the ratio of Ri (or average Ri) to, Ro (or average Ro). The prominence ratio is preferably less than 1.0. Preferably, this ratio is between about 0.70 and about 0.95; more preferably the ratio is between about 0.75 and about 0.90; and most preferably the ratio is between about 0.80 and about 0.90.
Eccentric non-uniform multi-lobed dimples may also have constant Ri and Ro. They may also have either varying Ri or varying Ro, or both. The prominence ratio for eccentric non-uniform multi-lobed dimples is defined similarly to the prominence ratio for concentric non-uniform multi-lobed dimples.
The dimple may comprise any number of lobes. For illustrative purposes, the dimple of the present invention is depicted to have between three and seven lobes.
The present invention is also directed to a golf ball having the multi-lobed dimples incorporated on its outer surface. In accordance to one aspect of the present invention, the multi-lobed dimples are arranged in a hexagonal array, wherein one multi-lobed dimple is surrounded by six multi-lobed dimples. The multi-lobed dimples are preferably arranged in an icosahedron pattern. The icosahedron pattern further comprises twelve vertex dimples, wherein each vertex dimple is surrounded by five multi-lobed dimples.
In accordance to another aspect of the present invention, the golf ball comprises uniform multi-lobed dimples and non-uniform multi-lobed dimples arranged in an icosahedron pattern. Preferably, the uniform lobed dimples occupy a substantial portion of the outer surface on the golf ball and the non-uniform multi-lobed dimples surround the vertex dimples to improve dimple coverage.
In accordance to another aspect of the present invention, the number of lobes of each multi-lobed dimple is the same as the number of dimples surrounding said multi-lobed dimple. Hence, each multi-lobed dimple in the hexagonal array comprises six lobes, and each vertex dimple comprises five lobes.
In accordance to another aspect of the present invention, the apex points of adjacent lobes straddle a line connecting the centers of adjacent dimples to maximize dimple coverage.
The multi-lobed dimples of the present invention improve the aerodynamic performance of a golf ball, because they provide greater dimple circumference on the golf ball than non-overlapping conventional circular dimples. They also provide higher dimple coverage, i.e., as much as about 93%, than dimensionally similar non-overlapping conventional circular dimples.